Examples of the secondary battery include a nickel-metal hydride battery, a lead secondary battery, and a lithium-ion secondary battery.
Such secondary batteries are used as power sources of portable information terminals typified by mobile phones. In particular, lithium-ion secondary batteries have been actively researched and developed because capacity thereof can be increased and size thereof can be reduced.
A lithium-ion secondary battery includes various members such as an electrode current collector, an electrode active material, an electrolyte solution, a separator, and an exterior body lead electrode, and is fabricated through a large number of steps. In view of use in a wide range of applications, low-cost fabrication is important; as materials to be used, the number of steps required for the fabricating, and time required for the fabricating are reduced, the fabricating cost can be suppressed.
Note that a negative electrode of a lithium-ion secondary battery is generally formed by application of an active material formed of a carbon material onto a negative electrode current collector. An active material refers to a material that relates to insertion and extraction of ions (lithium ions) that are carriers. An active material layer formed by application of an active material onto a current collector includes a conductive additive, a binder, and the like in addition to the active material in some cases.
For a material suitable for a negative electrode, lithium metal has favorable characteristics because of its low redox potential and high specific capacity per unit volume and per unit weight. However, in the secondary battery, lithium in an electrolyte solution is deposited in the form of dendrites (in the form of whiskers) on lithium metal at the time of charging and penetrates a separator, which causes a short circuit in some cases. Furthermore, basal portions of the dendrites (whiskers) are dissolved in the electrolyte solution at the time of discharging and isolated lithium is generated, leading to a problem of low cycle characteristics. Thus, in a lithium-ion secondary battery that has been in practical use, an active material formed of a carbon material is applied onto a current collector to form an active material layer, and occlusion and release of lithium ions are utilized as a reaction of a negative electrode (Non-Patent Document 1).
However, when an active material layer is formed, as apparatuses, many facilities such as a mixer for forming slurry, a coater for coating slurry, and a dryer for drying the slurry are needed. Furthermore, time for each step in which such an apparatus is used is required. Furthermore, members such as an active material, a conductive additive, and a binder are expensive. In the case of an electrode in which an active material layer is used, the potential of a cell is decreased by the reaction potential of an active material in the secondary battery, resulting in a decrease in energy density. Meanwhile, if a method in which lithium is directly deposited on a current collector is employed, a negative electrode has the lowest potential in all components in a secondary battery; thus, a secondary battery having a highest energy density can be fabricated.